Cinched jackets are a great look for plus-sized teens. They create a waist --- even if you do not really have one --- and help to minimize the stomach area.
You can also get this effect by adding a belt to a regular, button-down jacket. There are varieties of different looks that work well with a cinched jacket.
For example, a pair of dark, bootcut jeans and a solid-colored button-down top with a cinched jacket looks fabulously trendy. Make sure the top is longer than the jacket to attain an overall slimming effect.